OplsTorsionType.hpp

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 * [8] Bhattarai, Newman & Gezelter, Phys. Rev. B 99, 094106 (2019).
 */
 
/**
 * @file OplsTorsionType.hpp
 * @author    teng lin
 * @date  11/16/2004
 * @version 1.0
 */
 
#ifndef TYPES_OPLSTORSIONTYPE_HPP
#define TYPES_OPLSTORSIONTYPE_HPP
 
#include "types/PolynomialTorsionType.hpp"
 
namespace OpenMD {
 
  /**
   * @class OplsTorsionType OplsTorsionType.hpp "types/OplsTorsionType.hpp"
   * These torsion types are defined identically with functional form given
   * in the following paper:
   *
   * "Development and Testing of the OPLS All-Atom Force Field on
   * Conformational Energetics and Properties of Organic Liquids,"  by
   * William L. Jorgensen, David S. Maxwell, and Julian Tirado-Rives,
   * J. Am. Chem. Soc.; 1996; 118(45) pp 11225 - 11236;
   * DOI: 10.1021/ja9621760
   *
   * This torsion potential has the form:
   *
   *  \f[ V_{tors} = 0.5 (v_1 (1+\cos(\phi)) + v_2 (1-\cos(2 \phi)) + v_3
   * (1+\cos(3 \phi))) \f]
   *
   * Notes:
   *
   * 1. OpenMD converts internally to a Polynomial torsion type because
   *    all of the phase angles are zero in the OPLS paper.
   * 2. Coefficients are assumed to be in kcal / mol, and be careful about
   *    that factor of 1/2 when importing the coefficients!
   */
  class OplsTorsionType : public PolynomialTorsionType {
  public:
    OplsTorsionType(RealType v1, RealType v2, RealType v3, bool trans180) :
        PolynomialTorsionType(), v1_(v1), v2_(v2), v3_(v3) {
      // convert OPLS Torsion Type to Polynomial Torsion type
      RealType c0 = v2 + 0.5 * (v1 + v3);
      RealType c1 = 0.5 * (v1 - 3.0 * v3);
      RealType c2 = -v2;
      RealType c3 = 2.0 * v3;
 
      if (!trans180) {
        c1 = -c1;
        c3 = -c3;
      }
 
      setCoefficient(0, c0);
      setCoefficient(1, c1);
      setCoefficient(2, c2);
      setCoefficient(3, c3);
    }
 
    friend std::ostream& operator<<(std::ostream& os, OplsTorsionType& ott);
 
  private:
    RealType v1_;
    RealType v2_;
    RealType v3_;
  };
 
  std::ostream& operator<<(std::ostream& os, OplsTorsionType& ott) {
    os << "This OplsTorsionType has below form:" << std::endl;
    os << ott.v1_ << "/2*(1+cos(phi))"
       << " + " << ott.v2_ << "/2*(1-cos(2*phi))"
       << " + " << ott.v3_ << "/2*(1+cos(3*phi))" << std::endl;
    return os;
  }
 
}  // namespace OpenMD
 
#endif  // TYPES_OPLSTORSIONTYPE_HPP